wait, wait...we? Who is we? Can you speak for 300 million people? More to the point, can you speak for the military and spy agencies? I would think that its fairly clear that in order to safeguard America's rule, you can't very well be a nice-guy about it. It requires brutal work, and I wouldn't be so quick to class those people as "we". The best soldier/spook is a psychopath, they're efficient.
Now, are you telling me that out of several hundred thousand memebers of the military and intel services, not to mention foreign assests, you couldn't find half a dozen that would be willing to murder an innocent man to further America's interests? Sure you would, and that stands true for any country that serious about being a player on the world stage; Russia, China, Israel, Britain, Egypt etc.
Its not a conspiracy theory, because there's evidence. Furthermore, the story is not nearly so clean-cut as you think, there are strange little details cropping up all over the place. But just ask yourself, who stands to profit from this? This happened in the midst of the Abu Ghraib scandal, and it certainly diverted attention, at least for a little while. There was a huge outcry in the US, as in most Western nations. This lead to increased support, or atleast tolerance for the occupation and the US's "war on terrorism". But, as I said, read the previous thread on the subject for a summary of the inconsistancies.
It could very well have been the Russians, I don't know. But what seems rather certain at this point, is that it was not Zarquawi.